Ischemic or traumatic injuries to the brain or spinal cord often produce irreversible damage to central nervous system (CNS) neurons and to their processes. These injuries are major problems to society as they occur frequently, the damage is often severe, and at present there are still no effective pharmacological treatments for acute CNS injuries. Clinically, ischemic cerebral stroke or spinal cord injuries manifest themselves as acute deteriorations in neurological capacity ranging from small focal defects, to catastrophic global dysfunction, to death. It is currently felt that the final magnitude of the deficit is dictated by the nature and extent of the primary physical insult, and by a time-dependent sequence of evolving secondary phenomena which cause further neuronal death. Thus, there exists a theoretical time-window, of uncertain duration, in which a timely intervention might interrupt the events causing delayed neurotoxicity. However, little is known about the cellular mechanisms triggering and maintaining the processes of ischemic or traumatic neuronal death, making it difficult to devise practical preventative strategies. Consequently, there are currently no clinically useful pharmacological treatments for cerebral stroke or spinal cord injury.
In vivo, a local reduction in CNS tissue perfusion mediates neuronal death in both hypoxic and traumatic CNS injuries. Local hypoperfusion is usually caused by a physical disruption of the local vasculature, vessel thrombosis, vasospasm, or luminal occlusion by an embolic mass. Regardless of its etiology, the resulting ischemia is believed to damage susceptible neurons by impacting adversely on a variety of cellular homeostatic mechanisms. Although the nature of the exact disturbances is poorly understood, a feature common to many experimental models of neuronal injury is a rise in free intracellular calcium concentration ([Ca2+]i). Neurons possess multiple mechanisms to confine [Ca2+]i to the low levels, about 100 nM necessary for the physiological function. It is widely believed that a prolonged rise in [Ca2+]i deregulates tightly-controlled Ca2+-dependent processes, causing them to yield excessive reaction products, to activate normally quiescent enzymatic pathways, or to inactivate regulatory cytoprotective mechanisms. This, in-turn, results in the creation of experimentally observable measures of cell destruction, such as lipolysis, proteolysis, cytoskeletal breakdown, pH alterations and free radical formation.
The classical approach to preventing Ca2+ neurotoxicity has been through pharmacological blockade of Ca2+ entry through Ca2+ channels and/or of excitatory amino acid (EAA)—gated channels. Variations on this strategy often lessen EAA-induced or anoxic cell death in vitro, lending credence to the Ca2+-neurotoxicity hypothesis. However, a variety of Ca2+ channel- and EAA-antagonists fail to protect against neuronal injury in vivo, particularly in experimental Spinal Cord Injury (SCI), head injury and global cerebral ischemia. It is unknown whether this is due to insufficient drug concentrations, inappropriate Ca2+ influx blockade, or to a contribution from non-Ca2+ dependent neurotoxic processes. It is likely that Ca2+ neurotoxicity is triggered through different pathways in different CNS neuron types. Hence, successful Ca2+-blockade would require a polypharmaceutical approach.
As a result of investigations, I have discovered methods of reducing the damaging effect of an injury to mammalian cells by treatment with compounds to reduce the binding between N-methyl-D-aspartate (NMDA) receptors and neuronal proteins.